Installing an antenna should be planned and you should understand a bit about home construction before you get yourself into trouble.
Personally I grew up with a tv antenna in our attic. It was fine because we had older construction with rafters instead of new construction with trusses. Trusses use smaller sized lumber but they pre build them in a layout that increases their stability. Rafters are single pieces of wood that run from the ridge or peak of the roof down to the top plates of your walls to form a triangle. They allow much more room in the attic for attic antennas that might even need a rotator.
If you are roof mounting the main concerns I would have are first is the antenna grounded correctly. You do not want a fire or to blow out your television tuners. Even if lightning strikes close to the home and not the antenna directly you can still blow out your electronics because the antenna will pick up free electricity through the air.. that happens during every rain storm when electric lines on telephone poles have near strikes and large amounts of electricity is induced into the lines causing surges.
I would suggest that you use appropriate grounding wire… Standoffs that are insulated so the wire does not touch the building.. and once the antenna cable is inside your home you might want to pickup a surge protector used for networking that has a Network Cable connector. I can not speak about any dB loss but I do know they exist. If you need to have a powered distribution amp or power to your PreAmp inside your home it would be a great idea to run its electric through the surge protector and run the antenna line through it at the same time.
For mounting on a chimney you want to use a chimney mounting kit that will be a few steel straps that wrap around the chimney and create a stable mounting point. You do not want to drill into the chimney to mount the antenna or a pole directly.
If you are mounting directly to your roof using a stand you want to protect the roof from friction so you will want to install a piece of rubberized membrane over your shingles that has a layer of tar on it that will melt into the shingles and seal off your bolt holes.
You will want to make sure that you install your lag bolts directly into your rafters and not just into the plywood. If you must install a screw in a place where a rafter is not below it then you will need to build bracing inside the attic with 2×4 lumber below the area where you will mount the antenna. Plywood roofing will not take the stress of an antenna on its own.
I would suggest that you use either a outdoor rated acrylic silicon or straight silicon for caulking and you can pick up a calk tube of roofing cement for working on shingles, applying under flashing and other reasons.
When you are on the roof it is important to be careful.
- Have someone there to call for help if you fall.
- Bring your own cellphone and have it on.
- Extend the ladder about 4 feet above the roof edge so you can step off it onto the roof.
- Place the ladder in the corner of two roof lines where the gutter will support it on the side.
- Consider bungy cording the ladder to the gutter if you are alone so it will not fall leaving you on the roof with no way down.
- One hand on the ladder at all times especially when stepping on or off.
- Bring items up one at a time and do not overload yourself.
- Do not go closer than 2 feet to the edge.
- Step slowly on any roof you have not been on because roof sheathing rot can cause you to go through the roof even if the shingle look good.
- IF YOU FALL OR SLIP you want to flatten yourself out with your stomach to the roof and arms and legs spread out like you are making a snow angel face down. Friction will keep you from sliding.
- NEVER EVER EVER try to save something that is about to fall off the roof.. LET IT GO .. it is not worth slipping or being dragged down with it. let it go even if its your brand new phone.. well if its your wife give it a shot but other than that let it go.
Professionals wear rubber sole shoes specifically for working on roofs. At bare minimum you must wear soft sneakers that have very good stick and traction.
Professionals also use safety lines just like tree and mountain climbers.. you most likely won’t have this but if your situation warrants it you can rent these items at a good local supply center. Ask for a Safety Harness and Roof Mount Kit.. they do require screwing into your roof and will require repair when you are done.
I hope that helps you understand what you are in for when you get up on your roof. I worked in construction for many years and roofing was the only task that I had an agreement not to do. I would install the foundation to the trusses and help with the plywood roof decking but never the shingles we hired that out for safety and for insurance reasons. A small leak can ruin your drywall ceilings in less than an hour. I would do the work on my own home but not for hire.